Here's an example of where science meets society....and the result is a standoff. A story in the BBC points out growing resistance to an anti-obesity ad campaign launched by the organization Strong4Life in Atlanta, Georgia and designed to encourage overweight children to work on losing weight, because it can also make people feel bad about their weight.
Obesity is, for many at least, a cause of illness and limiting of quality of life. Traditionally, in human history, obesity was apparently rare because a regular surfeit of food just wasn't available, especially relative to the energy required to get the food in the first place. Genetic variation that was efficient at stowing away calories you didn't need right away, for future use, in the form of fat could perhaps have led to a survival and or fertility (or gestation or lactation) advantage and hence have been advanced by natural selection.
In some countries today, men feel proud to have fat wives and wives want to be fat to please their husbands, because it signals wealth and that he's a good caretaker. Nigerian 'fat farms' fatten up brides for this purpose.
But health-wise, if you're fit and trim, you'll feel better, more energetic, with more activity options open to you. And your life and health expectancy are better. These are statistical statements, not universals, but our media drive and tend to standardize quality judgments and imagery, and they generally give quite a different message.
In our rather passive lives today, where the media are the message, being overweight means not looking like pop stars, and hence not sexually desirable or not socially 'cool'. In our delicate states of mind, in which it seems everyone is on the verge of needing a personal therapist, we don't want anything or anyone to make us feel bad. Without rippled abs or various feminine curvatures, you are made to feel somehow inferior as a person. Since social judgments are subjective, and we mold them through advertising and fashion, being overweight may make you feel bad, but ads against it may make you feel even worse.
The facts about obesity, its causes and genetics, are quite complex as many MT posts have tried to point out. It's an example of a heavily studied problem that eludes simple answers, pointing out how difficult it it so understand this kind of causation, even if we are just focused on the technical issues of what you eat and what it does to you physically. Our scientific arrogance is matched to a great extent by our scientific ignorance.
Nonetheless, overall pronouncements from science about obesity have at least substantial if not perfect evidence behind them. But psychological feelings are also facts, also a part of health, and also as elusive as buttered eels. So when we try to implement pubic health, who decides what's best, and why, and for who?
We have no answers, but the questions are worth taking much more seriously than perhaps we do. And how do we decide what research is costly, problematic, and off the point in any case?